3 Answers
3

On new Macbook Pros, there is no microphone input. What you have is a line-level input. Microphones that do not have integrated power and amplification (all cheap computer microphones/handsets) will not work when connected to the line-level input.

The connectors are exactly the same, but on the line input there is stereo input and ground, and on the microphone input there is mono input, voltage reference and ground. The input level is also different, with line level at around 1V and microphone level at 10-100mV.

To resolve the problem, you need to get one of the following:

a USB sound card which has a proper microphone input circuitry,

a powered, amplified microphone that can be used with line-level input, or

As discussed in the "Are there headset adapters usable for MacBook Pros?" thread, new Macs DO have a normal Mic level input. However it is combined with the headphone jack (not the "audio in" port). You can purchase an adapter (such as the "Headset Buddy") that combines the headphone and mic into a single "smart-phone" style plug.

Note that this will only work properly under Mac OS. So if you intend to use your headset under Windows with BootCamp, you will want a USB adapter, such as the Griffin iMic instead.